The broad objective of this proposed research is to determine the mechanisms by which flavoproteins promote catalysis of oxidation-reduction and non-redox reactions. Specifically, the role of flavin in non-redox catalysis will be investigated by elucidating the reaction mechanism of D-hydroxynitrile lyase. Since this enzyme catalyzes a physiologically significant non-redox reaction but also exhibits properties similar to the flavoprotein oxidases, the relationship between the oxidase-like chemical reactivity of the prosthetic group and its ability to act as a catalyst in non-redox reactions will also be determined. Studies with pig liver glycolic acid oxidase will be conducted to determine the mechanism of hydrogen transfer and the role of flavin-substrate adducts as intermediates in oxidative catalysis by flavoproteins. The mechanism of action of these enzymes will be elucidated in studies involving: kinetic analysis, static and rapid reaction spectrophotometry, substrate analogues, flavin analogues containing modifications in the isoalloxazine nucleus and the N-10 side chain, radioactive tracers.